Optimum detector distance for neutron TOF (time-of-flight) temperature measurements.

摘要

Fuel ion temperatures for laser-driven, inertial-confinement fusion targets are often determined by neutron time-of-flight techniques. An optimum target-to-detector distance exists where the error in the temperature measurement is a minimum. Optimum distance depends on both target and detector characteristics. Equations are presented which relate the temperature error to the target ion temperature, the number of neutrons detected, and the detector temporal response. Sample calculations of temperature error and optimum detector distance for D-D and D-T plasmas are presented for typical Nova neutron time-of-flight detectors. They show that proper placement of a TOF detector is important for minimizing the temperature error for targets that have low neutron yields. For these detectors, temperature error becomes relatively insensitive to position for target yields above 10(sup 10) neutrons. Also, the analysis technique used to estimate signal broadening from recorded data is shown to be important for achieving statistically limited measurements. 2 refs., 11 figs., 5 tabs.